24 CULTIVATION AND GROWTH 



than by low oxygen (46). The adverse effect of flooding the soil on 

 the growth and survival of fungi is, however, believed to reflect a 

 deficit in oxygen (287, 288, 289). 



Very high oxygen pressure may somewhat reduce growth or change 

 the mycelial habit, but does not usually have a lethal effect (159, 

 328). 



Many discussions of aerobiosis in the fungi have confused growth 

 and fermentation. Numerous fungi ferment sugars anaerobically 

 (Chapter 7); this capacity has no essential bearing on growth, and 

 these forms should not be referred to as anaerobes. The term an- 

 aerobe, in fact, cannot be applied to any fungus; all require at least 

 some oxygen and none has as yet been reported to grow better at 

 low than at atmospheric oxygen pressure, although reducing substances 

 favor growth of Armillaria mellea (148). The vigorous anaerobic 

 fermentation of some aquatic phycomycetes (Chapter 7) is coupled 

 with a low oxygen demand and this relation is presumably a causal 

 one. 



9. CARBON DIOXIDE AND GROWTH 



Growth stimulation by carbon dioxide is considered later, with 

 carbon dioxide fixation (Chapter 7). High carbon dioxide pres- 

 sures generally inhibit the growth of fungi but the level at which 

 inhibiton appears is quite variable. Thus, Alternaria solani is mark- 

 edly inhibited by 38 mm of carbon dioxide (159) and Coniophora 

 cerebella by 23 mm (345), but many other fungi are only slightly 

 retarded in growth by carbon dioxide pressures of 150 mm or more 

 (12, 69, 117, 295). An isolate of Zygorhynchus vuilleminii found only 

 below the soil surface is retarded about 35 per cent by 152 mm of 

 carbon dioxide, while the surface soil inhabitant Penicillium nigri- 

 cans is completely inhibited under the same conditions (46). Finally, 

 we may mention Blastocladia pringsheimii, which grows well in an 

 atmosphere of tank carbon dioxide and which requires carbon dioxide 

 for the formation of resistant sporangia (85). 



10. WATER AND GROWTH 



The association of moisture and fungal growth is well known in 

 relation to the deterioration of natural and manufactured products. 

 Fungi require relatively high moisture levels, but most of the higher 

 fungi can grow in the absence of liquid water. 



